RFC 7230 section 3.2 indicates that HTTP header field names are case
insensitive.

Signed-off-by: David Edmondson <david.edmondson@oracle.com>
Message-Id: <20200224101310.101169-3-david.edmondson@oracle.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>
Signed-off-by: Max Reitz <mreitz@redhat.com>